Electron spectroscopy system with a multiple electrode electron lens

ABSTRACT

A source of X-radiation and a target under study are mounted on the Rowland circle of a crystal monochromator employed to focus a characteristic line of the X-radiation on the target. An electron lens with four electrodes for providing three independently variable electrical parameters is mounted in the photoelectron path between the target and an electron spectrometer adjusted to focus photoelectrons within a fixed energy range on a detector. The electrical parameters of this electron lens are adjusted to provide a target image of constant size and position at the entrance of the electron spectrometer while accelerating or decelerating photoelectrons from the target into the energy range for which the electron spectrometer is adjusted.

United States Patent [54] ELECTRON SPECTROSCOPY SYSTEM WITH A MULTIPLEELECTRODE ELECTRON LENS 23 Claims, 6 Drawing Figs.

[52] US. Cl ..250/49.5 AE, 250/419 ME, 250/49.5 A, 250/495 P [5 l] Int.Cl.. l-l0lj 37/00, GOln 23/00 [50] Field of Search 250/419 SE, 4l.9 ME,49.5 A, 49.5 C, 49.5 Pl

[ 56] References Cited UNITED STATES PATENTS 3,084,249 4/1963 Enge250/419 36 DETEC OR OTHER REFERENCES Photon Impact Studies of MoleculesUsing A Mass Spectrometer" By H. Hurzeler et al. from The Journal ofChemical Physics, Vol. 28, No. LJan. 1958, pp. 76- 82.

The Esca Method Using Monochomatic X-rays and A Permanent MagnetSpectrograph By A. Fahlman et al. From Arkiv For Fysik, Vol. 32, Paper7, 1966, pp. 111- 129.

lon Microprobe Mass Analyser By H. Liebl from the Journal Of AppliedPhysics, Vol. 38, No.- l3, Dec. I967, pp. 5277- 5283.

Primary Examiner-William Fv Lindquist Attorney-Roland l. GriffinABSTRACT: A source of X-radiation and a target under study are mountedon the Rowland circle of a crystal monochromator employed to focus acharacteristic line of the X-radiation on the target. An electron lenswith four electrodes for providing three independently variableelectrical parameters is mounted in the photoelectron path between thetarget and an electron spectrometer adjusted to focus photoelectronswithin a fixed energy range on a detector. The electrical parameters ofthis electron lens are adjusted to provide a target image of constantsize and position at the entrance of the electron spectrometer whileaccelerating or decelerating photoelectrons from the target into theenergy range for which the electron spectrometer is adjusted.

CRYSTAL MONOCHROMATOR ROWLAND CIRCLE PATENTEUNDV 2 SHEET 10F 2 ELECTRONSPECTROMETER CRYSTAL MON OCHROMATOR ROWLAND CIRCLE DETECTOR igure 1LECTRON LENS INVENTORS KAI MB. STEGBAHN EDWARD F. BARNETT ATTORNEYELECTRON SPECTROMETER PATENTEUNUV 2 SHEET 2 BF 2 ELEcTRD LENS PLANE OFRowLAND CIRCLE 2o ELECTRON SPECTROMETER w TARGET igure 5 ELECTRONSPECTROMETER S R O T N E V N ELECTRON LENS KAI MB.SIEGBAHN EDWARD F.BARNETT BY W ATTORNEY ELECTRON SPECTROSCOPY SYSTEM WITH A MULTIPLEELECTRODE'ELECTRON LENS BACKGROUND AND SUMMARY OF THE INVENTION Thisinvention relates to electron spectroscopy for chemical analysis(hereinafter referred to asESCA) and, more particularly, to improvedESCA systems employing multiple electrode electron lenses.

Typically, the main contributions to the width of an electron line in anESCA spectrum are the inherent width of the characteristicX-ray lineused to excite the electron emission and the inherent width of theatomic level under study. In order to obtainuseful information aboutatoms and molecules from ESCA, the width of the electronline shouldreflect only the inherent width of the atomic level under study. An ESCAsystem in which the width of the X-ray line used to excite the electronemission is prevented from contributing to the width 1 or 2. The angularspread with which photoelectrons enter the electron spectrometer in thecircumferential direction is limited in systems employing multipleelectrode electron lenses of the type described aboveby the aperturingeffect of the lens electrodes. Accordingly, it is another object of thisinvention to provide an improved ESCA system of that type in which theacceptance angle of the photoelectronsmay be increased in thecircumferential direction by as much as a factor of ten, therebysignificantly increasing the sensitivity of the system without impairingits resolution.

' This object is accomplished according to another preferred embodimentof this invention by employing a modified hemispherical electrodespectrometer with a conical entrance end having an axis of symmetry thatpassesthrough the center of the hemispherical electrodes and byemploying an electron lens having four pairs of conical fan-shapedelectrodes with of the electron line in the ESCA spectrum is describedand claimed in copending US Pat. application, Ser. No. .765,l40 entitledELECTRON SPECTROSCOPY SYSTEM WITH DISPERSION COMPENSATION, filed on Oct.4, 1968, by Kai Siegbahn, issued as,U.S. Pat. No. 3,567,926 on Mar. 2,I97 I and assigned to the same assignee as this patent application. Inthat system the dispersion of a crystal, monochromator used to focus acharacteristic X-ray line on a target is made equal to that of anelectron spectrometer used to focus photoelectrons emerging from theirradiated target on to a detector. The geometry of the system isarranged so that the dispersion of the electron spectrometer compensatesfor the dispersion of the crystal monochromator and thereby prevents thewidth of the X-ray line focusedon the target from adding to the width ofthe electron line focused on the detector. However, this can only beaccomplished for a relatively narrow electron energy range of about topercent of the op,- timum electron energy for dispersion compensation insuch a system. Accordingly, it is an object of this invention to providean improved ESCA system in which dispersion compensation may be employedfor a much wider energy range to prevent the width of the X-ray linefrom adding to the width of the electron line. I

This object is accomplished according to a preferred embodiment of thisinvention by employing an electron lens comprising four conicalring-shaped electrodes having a common axis of symmetry in thephotoelectron path between the target and the electron spectrometer.These electrodes are electrically insulated from each other to providethree independently variable electrical parameters. The focusing actionof this electron lens produces an image of the target at the entrance ofthe spectrometer. By adjusting the electrical parameters of the electronlens the size and position of this image may be maintained constantwhile accelerating or decelerating photoelectrons from the target intothe energy range for which the electron spectrometer is adjusted. Thissubstantially increases the energy range over which dispersioncompensation may be employed to prevent the width of the X-ray linefocused on the target from adding to the width of the electron linefocused on the detector.

ln ESCA systems employing electrostatic electron spectrometers withhemispherically shaped electrodes, greater sensitivity may be achievedfor a given absolute resolution by increasing the solid angle at whichphotoelectrons from the target enter the electron spectrometer. Thissolid angle is hereinafter referred to as the acceptance angle. It isapproximately proportional to the product of the angular spread of thephotoelectrons entering the electron spectrometer in the radialdirection (the direction in which the'photoelectrons are subsequentlydeflected and dispersed by the spectrometer) and the angular spread ofthe photoelectrons entering the electron spectrometer in thecircumferential direction (the direction normal to the radialdirection). Because of aberrations in the electron spectrometer, theangular spread with which photoelectrons enter the electron spectrometerin the radial direction must be kept very small, on the order of aboutthe same axis of symmetry as'the conical-entrance end of thehemispherical electrode spectrometer. These pairs of electrodes arepositioned so that their apertures are narrowest in the radial directionand broadest in the circumferential direction. The focusing actionof'the electron lens therefore occurs mainly, or entirely, in theradialdirection, thereby increasing the acceptance angle in thecircumferential direction and providing greater sensitivity fora givenabsolute resolution. Each of these pairs of electrodes is electricallyinsulated from the others to provide three independentlyvariableelectrical parameters for controlling the size and position ofthe target image and the kinetic energy of the photoelectrons enteringthe electron spectrometer.

BRIEF DESCRIPTION OF THE DRAWING tron lens having its axis of symmetryoriented at a finite angle 1 with respect to the plane of the Rowlandcircle.

FIG. 5 is a sectional elevational representation of an electron lens andspectrometer that may be used to provide an improveddispersion-compensated ESCA system according to another preferredembodiment of this invention.

FIG. 6 is an elevational representation of the electron lens andspectrometer of FIG. 5 as viewed in a plane perpendicular to the planeof FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there isshown a dispersion-compensated ESCA system for use in studying thechemical composition of a selected target 10. This system includes afixedly mounted source 12 for emitting a beam of X-radiation 14 along afirst axis 16. Source 12 may be constructed, for example, as describedon pages 178-179 of the book ESCAwritten by Kai Siegbahn et al. andpublished in Dec. 1967, by Almqvist andWicksells Boktryckeri AB(hereinafter referred to as the book ESCA). A dispersing crystal 18 of acrystal monochromator isfixedly mounted on the first axis 16 in the pathof the X-radiation l4. Dispersing crystal 18 is provided with a curvedsurface so that the atomic layers have a radius equal to the diameter ofthe Rowland circle 20. The dispersion of the crystal monochromator(caused by Bragg reflection within dispersing crystal 18) produces aspectrum of the X- radiation 14. A characteristic line 22 of this X-rayspectrum is focused by the crystal monochromator along a second axis 24making an angle B of about 22 with the first axis 16. Target 10 isremovably mounted on the second axis 24 in thepath of thischaracteristic X-ray line 22. Both target 10 and source 12 are mountedon the Rowland circle 20 of the crystal monochromator.

The irradiation of target 10 by the characteristic X-ray line 22 causesphotoelectrons to emerge from the target along a third axis 26 making anangle +'y 1 (see FIG. 3) of about 75 with the second axis 24. Due to thedispersion of the crystal ty and resolution of the system. By adjustingthe potential difference V V between lens electrodes 40 and 42 and thepotential difference V V between lens electrodes 40 and 44, the size andposition of image 48 may be selected and, in addice lerated ordecelerated into the range for which electron spectrometer 28 isadjusted.

An image 48 of target is produced at the entrance end of electronspectrometer 28 by the focusing action of electron monochromator, thecharacteristic X-ray line 22 has a finite 5 tion, maintained constant toprovide the system with maxline width that causes photoelectrons fromthe same energy imum sensitivity and resolution irrespective of theinitial level but different parts of the target to emerge with differentkinetic energy of the photoelectrons being decelerated or acenergies.For example, as indicated in FIG. 1, a higher energy celerated into theenergy range for which spectrometer 28 is photon strikes target 10 tothe right (as viewed in the beam adjusted. direction of thecharacteristic X-ray line) of a lower energy 10 In order to preventthewidth of the characteristic X-ray line photon and producesphotoelectrons of higher energy (E,+A 22 from adding to the width of theelectron line focused on de- E) than the photoelectrons of energy (E,AE)produced by tector 36, the overall dispersion of electron lens 38 andelecthe lower energy photon. tron spectrometer 28 is made to cancel thedispersion of the As shown in FIGS. 1 and 2, an elec ron disp r ngdevice, crystal monochromator. This is achieved by arranging the such asan electron spectrometer 28 fixedly mounted with iIS geometry of thesystem and choosing the electrical parameters entrance end on the thirdaxis 26, is employed for analyzing so th t; photoelectrons from theirradiated target 10. Electron specp sin a Sin E trometer 28 maycomprise, for example, an electrostatic spec- 7 tan 0 trometer withhemispherical electrodes 32 and 34, such as the i 7 one represented inFIGS- 1 and or a semicircular magnetic "hi this equation (as indicatedwith the air of FIGS. land 3); spectrometer, such as the one shown anddescribed in connecp equals the mean radius f Spectrometer 2 tion withSection Vlll:3 on pages 182 et seq. of the book Requals the radius fR ld circle 0; ESCA. In any case, electron spectrometer 28 is adjusted suchM equa15the magnification ofejectt-oh lens as by operating itselectrodes 32 and 34 at selected potentials 6 equals the Bragg angle(the angle between the second axis V and V respectively, to focus afixed and relatively narrow 24 and a tangent to the Rowland circle 20 ata point ihtep energy range of the photoelectrons (for example, aboutlOev. sected by this Second axis); out of about 1,500ev.) onto adetector 36 mounted at the exlt q) equals the angle between the thirdaxis 26 and the end of the electron spectrometer. Detector 36 maycomprise a radiated surface of target 10; fixedly'moumed phfnomumphertube or a removably -y equals the angle between the irradiated surfaceof target g photograph: plate as represemed Schemaucany m 10 and atangent to the Rowland circle 20 at a point inter- An electron lens 38is fixedly mounted along the third axis zzz g zggii f Second axls 24 andthe "radiated Sur 26 between target 10 and the entrance end of electronspec- E equals the kinetic energy of the central electron my in trometer28 to accelerate or decelerate photoelectrons from Spectrometer and thetarget into the energy range for which the electron spec- E equals themean e'hergy of the photons in the charac trometer is adjusted. Electronlens 38 comprises four conical teristic X ray he 22 ring-Shapedelectrodes 46 symmeiricauy posi' From the above equation it may be seenthat for a given tloned about and spaced along the third axls 26 withthe smalgeometry and ratio of E8 to El dispersion compensation apertureadjacent to target 10 and a larger apenure 40 re uires that the manification M of electron lens 38 and jacent to the entrance end ofelectron spectrometer 28. These twice the Size of g at mm 48 be k t t tth four electrodes 40, 42, 44, and 46 are electrically insulated g g6 ePas from each other and o erated at inde endentl controllable range ofmmal. photoeiectrmi .energies be w p p d. As described above thls lsaccom llshed b ad ustln potentials V V V and V so that the potentlaldlfference l d J V -V between electrodes 40 and 42, the potentialdifference 5 t e q i gig I erencetsl 5 i V -,V; between electrodes 40and 44, and the potential dif- Rotenua l Hence 315.3 Juste to varyt erange 0 mlference V V between electrodes 40 and 46 ma be indeenphoioeleqmn energles bemg analyzed 3 y p A dlsperslon-compensated ESCAsystem of the type dently varled. The potentials V and V of thespectrometer d d b h b h h f electrodes 32 and 34, respectively, shouldbe chosen so that 8 We as been Wm t e lmenslons Set on m the central rayof the electrons passing through the spectrome- 50 h table (the a fa ndrepresent, the ter follows an equipotential surface of the samepotential V as gnudma] dlmenslons and dlameiersf respecnvely of theclosest lens electrode 46, This condition determines a electronic asshown for greaterclamym H04): positive value for the potentialdifference V,\/ between the inner spectrometer electrode 32 and theclosest lens electrode (p 5.0"; b= 0.5" r,=l .0" 46 and a negative valuefor the potential difference V V 55 Pa c= r,=2.0:: between the outerspectrometer electrode 34 and the closest 3; 3: 2:8,, lens electrode 46.The potential difference V -V between the electrode 40 closest to target10, which is operated at the =30 same potential V; as electrode 40 andthe electrode 46 closest to the entrance end of electron spectrometer 28controls the 5 5 5 ratio of the final to the initial kinetic energy ofphotoelectrons emerging from the target 10 and passing through theelectron Dispersion compensation has been achieved in this systemspectrometer 28. By adjusting this potential difference V.,V atdeceleration ratios E,/E, of, for example, one-third andonephotoelectrons having initial kinetic energies over a wide sixth, byoperating the electron spectrometer and lens elec- E../E,, Vi. v. \z, v.V v. \4. v. \'5, v. v. Ei. w. E... w.

1/3 -264 402 0 680 -355 -34li 510 170 1/6 774 -lll-. (I 1,000 -770 8501,020 17" range (for example, about 300 to 1,500 ev.) can be ac- 7Otrodes at the potehtials set forth in the table below (where E, is

the mean kinetic energy of those photoelectrons, as they leave thetarget, that pass through the spectrometer):

The electron lens 38 employed in the system of FIG. 1 may be entirelyelectrostatic or it may have both electrostatic and lens 3 8.Th e sizeand po sition ofimage affect the sensitivi magnetic components.Moreover, the electron lens 38 may be mounted so that its axis ofsymmetry is positioned in the plane of the Rowland circle 20 or, asindicated in FIG. I, at a finite angle with respect to the plane of theRowland circle 20, as indicated by dashed lines in FIG. 4. The latteralternativemay be used to advantage in systems where the electronlens 38would otherwise absorb large amounts of the X-radiation 14 before itreaches the target 10.

For greatest sensitivity the acceptance angle of electron spectrometer28 should be centered on the axis along which the highest photoelectronemission per unit solid angle with the least loss of monochromatizationis achieved. This axis is perpendicular to the plane of the Rowlandcircle for a gaseous target in which photoelectrons may be producedthroughout the entire region along the arc of the Rowland circlesubtended by the characteristic X-ray line 22. For such a gaseous targetit is therefore especially advantageous to mount the electron lens 38and spectrometer 28 so that the central ray, of the photoelectrons 30accepted'thereby isperpendicular to the plane of the Rowland circle 20,as indicated by solid lines in FIG. 4. These same considerations areequally applicableto the use of electron spectrometer 28 in an ESCAsystem not employing an electron lens 38.

Electron lens 52 comprises four pairs of conical fan-shaped A electrodes62, 64, 66, and having the same axisof symmetry 60 as the conicalentrance end 58 of electron spectrometer 50. These pairs of electrodes62, 64, 66, and 68 are electrically insulated from each other andoperated at independently adjustable potentials V V V and V respectively, to provide three independently variable potential dif ferences V,-Vbetween the first and second pairs 62 and.64, V V between the first andthird pairs 62 and 66, and V V.

between the first and fourth pairs 62 and 68. By adjusting,

these three independently variable potential differences the size andposition of the target image and the kinetic energy of thephotoelectrons entering electron spectrometer 50 may be controlled toprovide dispersion compensation for an extended energy range asdescribed above in connection with FIG. 1.

Electron lens 52 is fixedly mounted with its smallest conical apertureadjacent to target 10 and with its largest conical aperture adjacent tothe conical entrance end 58 of electron spectrometer 50. The conicalapertures of electron lens 52 are narrowest in the radial direction andbroadest in the circumferential direction so that the focusing action ofthe electron lens occurs mainly, or entirely, in the radial directionand only slightly, if at all, in the circumferential direction. This hasthe effect of increasing the acceptance angle in the circumferentialdirection, thereby providing greater spectrometer sensitivity for agiven absolute resolution.

ideally, the target 10 should lie on a conical surface thatintersectsthe adjacent surfaces of electrode pair 62 at right angles and thatpasses through, or is near to, .the axis of symmetry 60 of electron lens52. The closer target 10 is to theaxis of symmetry 60 of electron lens52, the greater the reduction in aberrations that may be achieved. Allof the rays of the photoelectrons accepted by electron lens 52 arenearly normal to the conical surfaces forming the edges of the lensapertures and the entrance end 58 of the electron spectrometer 50. Thisalso helps to reduce aberrations. Electron lens 52 produces an image ofthe accepted rays in a cone 70 passing through the center C of thehemispherical electrodes 54 and 56.

We claim:

I. An electron spectroscopy system comprising:

a source for producing a beam of electromagnetic radiation along a firstaxis; v

a monochromator including a dispersing element positioned on the firstaxis in the path of said electromagneticradiation, said monochromatorfocusing a portion of this.electromagnetic radiation along a second axisonto a target positioned on the second axis and substantially on theRowland circle of the monochromator thereby producing electron emissionfromthe irradiated target along a third axis;

a detector;

an electron dispersing device positioned on the third axis in the pathof this electron emission, said electron dispersing device focusingelectrons from the irradiated targetonto the detector; and

an electron lens forming an image of the irradiated target with theelectrons ,from this imagepassing through the electron dispersingdevice, said electronlens including at least-four'focusing elementspositioned along the third axis in the electron path between the targetand the electron dispersing device to provide at leastthreeindependently variable electrical parameters for controlling the sizeand position of the image and thedifference between the initial andfinal kinetic energies of the electrons passingthrough the electronlens.

2. An electron spectroscopy system as in claim I wherein said focusingelements comprise generally conical, ringshaped electrodes electricallyinsulated from each other and independently operable at differentelectrical potentials, said electrodes being symmetrically positionedabout and spaced along the third axis with their narrowest aperturepositioned adjacent to the target and a larger aperture positionedadjacent to the electron dispersing device.

3. An electron spectroscopy system asinclaim 2 wherein:

said source is positioned substantially on the Rowland circle of themonochromator;

said electromagnetic radiation is X-radiation, the portion of saidelectromagnetic radiation beingfocused onto the target comprising acharacteristic line of this X-radiation; and

the overall dispersion of the electron lens and the electron dispersingdevice is made to cancel the dispersion of the monochromator to reducethe contribution of the characteristic X-ray line width to the linewidth of the electrons focused onto the detector.

4. An electron spectroscopy system as in claim lwherein:

said electron dispersing device comprises an electronspectrometer havingapair of hemispherical electrodes electrically insulated from each otherand operable at dif ferent electrical potentials, said electronspectrometer having agenerally conical-shaped entrance end with. an axisof symmetry passing through the-center of the hemispherical electrodes;and

said focusing elements comprise four pairs of generally conical,fan-shaped electrodes electrically insulated from each other andindependently operable at differentelectrical potentials, said pairs offan-shaped electrodes having the same axis of symmetry as theconically-shaped entrance end of the spectrometer and being spaced apartwith their smallest conical aperture positioned adjacent to the targetand their largest conical aperture positioned adjacent to theconically-shaped entrance end of the electron spectrometer.

5. An electron spectroscopy system as in claim- 4. wherein the image ofthe irradiated target is formed by the electron lens at the conicallyshaped entrance end of the electron spectrometer in a cone having itsapex located at the center of the hemispherical electrodes.

6. An electron spectroscopy system as in claim 5 wherein:

said source is positionedsubstantially on the Rowland circle of themonochromator;

said electromagnetic radiation is X-radiation, the portion of saidelectromagnetic radiation being focused onto the target comprising acharacteristic line of this X-radiation; and

the overall dispersion of the electron lens and the electronspectrometer is made to cancel the dispersion of the monochromator toreduce the contribution of the characteristic X-ray line width to theline width of the electrons focused onto the detector.

7. An electron spectroscopy system as in claim 1 wherein the electronlens has an axis of symmetry positioned in the plane of the Rowlandcircle of the monochromator.

8. An electron spectroscopy system as in claim 1 wherein the electronlens has an axis of symmetry positioned at a finite angle with respectto the plane of the Rowland circle of the monochromator. v

9. An electron spectroscopy system as in claim 8 wherein the axis ofsymmetry of the electron lens is positioned perpendicular to the planeof the Rowland'circle of the monochroma- {OR 10. An electronspectroscopy system as in claim 1 wherein the overall dispersion of theelectron lens and the electron dispersing device cancels out thedispersion of the monochromator.

11. An electron spectroscopy system as in claim 1 wherein said focusingelements comprise at least four electrodes electrically insulated fromeach other and independently operable at different electrical potentialswith the potential differences between a first and a second, the firstand a third, and the first and a fourth of these electrodes beingadjustable to control the size and position of the image of theirradiated target and the ratio of the final to the initial kineticenergy of the electrons emitted from the irradiated target and passingthrough the electron dispersing device.

12. An electron spectroscopy system as in claim 1 wherein:

said source is positioned substantially on the Rowland circle of themonochromator;

said electromagnetic radiation is X-radiation, the portion of saidelectromagnetic radiationbeing focused onto the target comprising acharacteristic line of this X-racliation; and

the overall dispersion of the electron lens and the electron dispersingdevice is made equal in magnitude to and opposite in sign from thedispersion of the monochromator so that these dispersions cancel.

13. An electron spectroscopy system as in claim 12 wherein:

said electron dispersing device comprises an electron spectrometerhaving a pair of hemispherical electrodes electrically insulated fromeach other for operation at different electrical potentials;

said source, monochromator, target, electron spectrometer,

and electron lens are arranged so that p SinOSinrbE,

tan 0, where p equals the mean radius of the hemispherical electrodes ofthe electron spectrometer, R equals the radius of the Rowland circle ofthe monochromator, M equals the magnification of the electron lens,equals the angle between the second axis and a tangent to the Rowlandcircle at a point intersected by the second axis and by the irradiatedsurface of the target, 1 equals the angle between the third axis and theirradiated surface of the target, 7 equals the angle between theirradiated surface of the target and a tangent to the Rowland circle ofthe monochromator at a point intersected by the second axis and by theirradiated surface of the target, E, equals the kinetic energy of thecentral electron ray in the electron spectrometer, and E equals the meanenergy of the photons in the characteristic line of the X radiation.

14. An electron spectroscopy system as in claim 12 wherein said focusingelements comprise at least four electrodes electrically insulated fromeach other and independently operable at different electrical potentialswith the potential differences between a first and a second, the firstand a third, and the first and a fourth of these electrodes beingadjustable to control the size and position of the image of the targetand the ratio of the final to the initial kinetic energy of theelectrons emitted from the irradiated target and passing through theelectron spectrometer.

15. An electron spectroscopy system as in claim 12 wherein said focusingelements comprise at least four generally ringshaped electrodes spacedalong the third axis and electrically insulated from each other foroperation at independently adjustable electrical potentials.

16. An electron spectroscopy system as in claim 12 wherein:

said electron dispersing device comprises an electron spectrometeroperated to focus electrons within a selected energy range onto thedetector; and

said focusing elements comprise at least four electrodes spaced alongthe third axis and operated at independently adjustable electricalpotentials to maintain the size and position of the image of theirradiated target constant while accelerating or decelerating electronsfrom the irradiated target into the selected energy range of theelectron spectrometer.

17. An electron spectroscopy system as in claim 16 wherein said electronspectrometer comprises a pair of hemispherical electrodes operated atindependently adjustable electrical potentials to focus electrons withinthe selected energy range onto the detector.

18. An electron spectroscopy system comprising:

a source for producing a beam of electromagnetic radiation along a firstaxis;

a monochromator including a dispersing element positioned along thefirst axis in the path of this electromagnetic radiation to project aportion thereof along a second axis onto a target positioned along thesecond axis and substantially on the Rowland circle of the monochromatorand thereby produce electron emission from the irradiated target along athird axis;

a detector;

an electron dispersing device positioned along the third axis in thepath of this electron emission to focus electrons from the irradiatedtarget onto the detector; and

an electron lens positioned along the third axis between the irradiatedtarget and the electron dispersing device in the path of this electronemission to form an image of the irradiated target adjacent to theelectron dispersing device with the electrons from this image passingthrough the electron dispersing device, said electron lens includingmeans for adjusting the size and position of the image of the irradiatedtarget and means for independently adjusting the ratio of the final tothe initial kinetic energy of the electrons emitted from the irradiatedtarget and passing through the electron dispersing device.

19. An electron spectroscopy system as in claim 18 wherein said meanscomprise at least four electrodes positioned along the third axisbetween the irradiated target and the electron dispersing device in thepath of the electron emission, said electrodes being electricallyinsulated from each other for operation at independently adjustableelectrical potentials.

20. An electron spectroscopy system as in claim 19 wherein:

said electrodes are operable at different electrical potentials; and

the potential differences between a first and a second, the

first and a third, and the first and a fourth of said electrodes areadjusted to control the size and position of the image of the irradiatedtarget and the ratio of the initial to the final kinetic energy of theelectrons emitted from the irradiated target and passing through theelectron dispersing device.

21. An electron spectroscopy system as in claim 20 wherein:

said source comprises a source of X-radiation positioned substantiallyon the Rowland circle of the monochromator;

said electromagnetic radiation comprises X-radiation with the portionprojected onto the target comprising a characteristic line thereof;

said electron dispersing device comprises an electron spectrometer; and

the potential differences between the first and the second, the firstand the third, and the first and the fourth of said electrodes areadjusted to make the overall dispersion of the electron lens and theelectron spectrometer substantially equal in magnitude to and oppositein sign from the dispersion of the monochromator so that thesedispersions cancel and thereby reduce the contribution of thecharacteristic X-ray line width to the line width of the electronsfocused onto the detector. 22. An electron spectroscopy system as inclaim 1 wherein: said electron spectrometer is operated to focuselectrons within a selected energy range onto the detector; and

said electrodes are independently adjustably operated to maintain thesize and position of the image of the irradiated target constant whileaccelerating or decelerating electrons from the irradiated target intothe selected energy range of the electron spectrometer.

23. An electron spectroscopy system as in claim 18 wherein said electronlens and said electron spectrometer have an overall dispersion adjustedto cancel the dispersion of the monochromator.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,617741 Dated Ngyembe: 2 122],

Inv n (s) lggi 14,5, fiiegbghn and Edyard FLBarnett It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 3, line 3, "75 should read 70 Column 4, line 21, "air" shouldread aid line 67, "E /E should read E /E lines 67-69, the table listedshould be placed immediately below line 73;

Column 5, line 19, cancel "30";

Column 9, line 10, "1'' should read 21 Signed and sealed this 2nd day ofMa 1972.

r SEAL) Attest:

EDWARD M.'FLETCHER,JR. ROBERT GOTTSCHALK attesting Officer Commissionerof Patents DRM PO-IOSO (10-59) USCOMM-DC 60375-P59 fl US, GOVERNMINTPRINTING OFFICE H69 0-366-"4 160010

1. An electron spectroscopy system comprising: a source for producing abeam of electromagnetic radiation along a first axis; a monochromatorincluding a dispersing element positioned on the first axis in the pathof said electromagnetic radiation, said monochromator focusing a portionof this electromagnetic radiation along a second axis onto a targetpositioned on the second axis and substantially on the Rowland circle ofthe monochromator thereby producing electron emission from theirradiated target along a third axis; a detector; an electron dispersingdevice positioned on the third axis in the path of this electronemission, said electron dispersing device focusing electrons from theirradiated target onto the detector; and an electron lens forming animage of the irradiated target with the electrons from this imagepassing through the electron dispersing device, said electron lensincluding at least four focusing elements positioned along the thirdaxis in the electron path between the target and the electron dispersingdevice to provide at least three independently variablE electricalparameters for controlling the size and position of the image and thedifference between the initial and final kinetic energies of theelectrons passing through the electron lens.
 2. An electron spectroscopysystem as in claim 1 wherein said focusing elements comprise generallyconical, ring-shaped electrodes electrically insulated from each otherand independently operable at different electrical potentials, saidelectrodes being symmetrically positioned about and spaced along thethird axis with their narrowest aperture positioned adjacent to thetarget and a larger aperture positioned adjacent to the electrondispersing device.
 3. An electron spectroscopy system as in claim 2wherein: said source is positioned substantially on the Rowland circleof the monochromator; said electromagnetic radiation is X-radiation, theportion of said electromagnetic radiation being focused onto the targetcomprising a characteristic line of this X-radiation; and the overalldispersion of the electron lens and the electron dispersing device ismade to cancel the dispersion of the monochromator to reduce thecontribution of the characteristic X-ray line width to the line width ofthe electrons focused onto the detector.
 4. An electron spectroscopysystem as in claim 1 wherein: said electron dispersing device comprisesan electron spectrometer having a pair of hemispherical electrodeselectrically insulated from each other and operable at differentelectrical potentials, said electron spectrometer having a generallyconical-shaped entrance end with an axis of symmetry passing through thecenter of the hemispherical electrodes; and said focusing elementscomprise four pairs of generally conical, fan-shaped electrodeselectrically insulated from each other and independently operable atdifferent electrical potentials, said pairs of fan-shaped electrodeshaving the same axis of symmetry as the conically-shaped entrance end ofthe spectrometer and being spaced apart with their smallest conicalaperture positioned adjacent to the target and their largest conicalaperture positioned adjacent to the conically-shaped entrance end of theelectron spectrometer.
 5. An electron spectroscopy system as in claim 4wherein the image of the irradiated target is formed by the electronlens at the conically shaped entrance end of the electron spectrometerin a cone having its apex located at the center of the hemisphericalelectrodes.
 6. An electron spectroscopy system as in claim 5 wherein:said source is positioned substantially on the Rowland circle of themonochromator; said electromagnetic radiation is X-radiation, theportion of said electromagnetic radiation being focused onto the targetcomprising a characteristic line of this X-radiation; and the overalldispersion of the electron lens and the electron spectrometer is made tocancel the dispersion of the monochromator to reduce the contribution ofthe characteristic X-ray line width to the line width of the electronsfocused onto the detector.
 7. An electron spectroscopy system as inclaim 1 wherein the electron lens has an axis of symmetry positioned inthe plane of the Rowland circle of the monochromator.
 8. An electronspectroscopy system as in claim 1 wherein the electron lens has an axisof symmetry positioned at a finite angle with respect to the plane ofthe Rowland circle of the monochromator.
 9. An electron spectroscopysystem as in claim 8 wherein the axis of symmetry of the electron lensis positioned perpendicular to the plane of the Rowland circle of themonochromator.
 10. An electron spectroscopy system as in claim 1 whereinthe overall dispersion of the electron lens and the electron dispersingdevice cancels out the dispersion of the monochromator.
 11. An electronspectroscopy system as in claim 1 wherein said focusing elementscomprise at least four electrodes electrically insulated from each otherand independently opErable at different electrical potentials with thepotential differences between a first and a second, the first and athird, and the first and a fourth of these electrodes being adjustableto control the size and position of the image of the irradiated targetand the ratio of the final to the initial kinetic energy of theelectrons emitted from the irradiated target and passing through theelectron dispersing device.
 12. An electron spectroscopy system as inclaim 1 wherein: said source is positioned substantially on the Rowlandcircle of the monochromator; said electromagnetic radiation isX-radiation, the portion of said electromagnetic radiation being focusedonto the target comprising a characteristic line of this X-radiation;and the overall dispersion of the electron lens and the electrondispersing device is made equal in magnitude to and opposite in signfrom the dispersion of the monochromator so that these dispersionscancel.
 13. An electron spectroscopy system as in claim 12 wherein: saidelectron dispersing device comprises an electron spectrometer having apair of hemispherical electrodes electrically insulated from each otherfor operation at different electrical potentials; said source,monochromator, target, electron spectrometer, and electron lens arearranged so that Rho equals the mean radius of the hemisphericalelectrodes of the electron spectrometer, R equals the radius of theRowland circle of the monochromator, M equals the magnification of theelectron lens, theta equals the angle between the second axis and atangent to the Rowland circle at a point intersected by the second axisand by the irradiated surface of the target, phi equals the anglebetween the third axis and the irradiated surface of the target, gammaequals the angle between the irradiated surface of the target and atangent to the Rowland circle of the monochromator at a pointintersected by the second axis and by the irradiated surface of thetarget, Es equals the kinetic energy of the central electron ray in theelectron spectrometer, and EP equals the mean energy of the photons inthe characteristic line of the X radiation.
 14. An electron spectroscopysystem as in claim 12 wherein said focusing elements comprise at leastfour electrodes electrically insulated from each other and independentlyoperable at different electrical potentials with the potentialdifferences between a first and a second, the first and a third, and thefirst and a fourth of these electrodes being adjustable to control thesize and position of the image of the target and the ratio of the finalto the initial kinetic energy of the electrons emitted from theirradiated target and passing through the electron spectrometer.
 15. Anelectron spectroscopy system as in claim 12 wherein said focusingelements comprise at least four generally ring-shaped electrodes spacedalong the third axis and electrically insulated from each other foroperation at independently adjustable electrical potentials.
 16. Anelectron spectroscopy system as in claim 12 wherein: said electrondispersing device comprises an electron spectrometer operated to focuselectrons within a selected energy range onto the detector; and saidfocusing elements comprise at least four electrodes spaced along thethird axis and operated at independently adjustable electricalpotentials to maintain the size and position of the image of theirradiated target constant while accelerating or decelerating electronsfrom the irradiated target into the selected energy range of theelectron spectrometer.
 17. An electron spectroscopy system as in claim16 wherein said electron spectrometer comprises a pair of hemisphericalelectrodes operated at independently adjustable electrical potentials tofocus electrons within the selected energy range onto the detector. 18.An electron spectroscopy system comprising: a sourcE for producing abeam of electromagnetic radiation along a first axis; a monochromatorincluding a dispersing element positioned along the first axis in thepath of this electromagnetic radiation to project a portion thereofalong a second axis onto a target positioned along the second axis andsubstantially on the Rowland circle of the monochromator and therebyproduce electron emission from the irradiated target along a third axis;a detector; an electron dispersing device positioned along the thirdaxis in the path of this electron emission to focus electrons from theirradiated target onto the detector; and an electron lens positionedalong the third axis between the irradiated target and the electrondispersing device in the path of this electron emission to form an imageof the irradiated target adjacent to the electron dispersing device withthe electrons from this image passing through the electron dispersingdevice, said electron lens including means for adjusting the size andposition of the image of the irradiated target and means forindependently adjusting the ratio of the final to the initial kineticenergy of the electrons emitted from the irradiated target and passingthrough the electron dispersing device.
 19. An electron spectroscopysystem as in claim 18 wherein said means comprise at least fourelectrodes positioned along the third axis between the irradiated targetand the electron dispersing device in the path of the electron emission,said electrodes being electrically insulated from each other foroperation at independently adjustable electrical potentials.
 20. Anelectron spectroscopy system as in claim 19 wherein: said electrodes areoperable at different electrical potentials; and the potentialdifferences between a first and a second, the first and a third, and thefirst and a fourth of said electrodes are adjusted to control the sizeand position of the image of the irradiated target and the ratio of theinitial to the final kinetic energy of the electrons emitted from theirradiated target and passing through the electron dispersing device.21. An electron spectroscopy system as in claim 20 wherein: said sourcecomprises a source of X-radiation positioned substantially on theRowland circle of the monochromator; said electromagnetic radiationcomprises X-radiation with the portion projected onto the targetcomprising a characteristic line thereof; said electron dispersingdevice comprises an electron spectrometer; and the potential differencesbetween the first and the second, the first and the third, and the firstand the fourth of said electrodes are adjusted to make the overalldispersion of the electron lens and the electron spectrometersubstantially equal in magnitude to and opposite in sign from thedispersion of the monochromator so that these dispersions cancel andthereby reduce the contribution of the characteristic X-ray line widthto the line width of the electrons focused onto the detector.
 22. Anelectron spectroscopy system as in claim 1 wherein: said electronspectrometer is operated to focus electrons within a selected energyrange onto the detector; and said electrodes are independentlyadjustably operated to maintain the size and position of the image ofthe irradiated target constant while accelerating or deceleratingelectrons from the irradiated target into the selected energy range ofthe electron spectrometer.
 23. An electron spectroscopy system as inclaim 18 wherein said electron lens and said electron spectrometer havean overall dispersion adjusted to cancel the dispersion of themonochromator.